The purpose of the proposed research is to identify the mechanism by which the lymphocytosis-promoting factor (LPF) from B. pertussis exerts its effect, not only in causing lymphocytosis but also with respect to its other activities as histamine-sensitizing factor and as a potent mitogen for murine T-cells which also results in the generation of non-specific cytotoxic lymphocytes. In addition, the activity of LPF as a mitogen for human lymphocytes will be explored. The relationship between LPF and other products of B. pertussis responsible for 1) adjuvanticity for conventional antibody formation as well as for homocytotropic antibody production and 2) protection against clinical pertussis will be explored. B. pertussis also enhances delayed hypersensitivity and experiments on the potential use of B. pertussis for immunotherapy of tumors are being carried out using mouse melanoma as the model system.